Refining lead



" be stirred and the a rotating drum,

Patented Aug. 30, 1927.

PHILIP W. DAVIS, OF CAMBRIDGE, MASSACHUSETTS.

' murmurs LEAD.

No Drawing.

The present invention relates to an improvem'ent 1n refinlng lead.

The process of the patent granted to me December 15, 1925, No. 1,566,078, contemplates broadly the exposure ofmolten lead alloys to intimate contact with molten litharge in bodies of small dimensions, irrespective of the temperature at which the reaction is performed. When the react-ion temperature is high, however, the wear on the lining of the container, whichmustbe basic, such as magnesite, is greater than when the temperature is lower. Furthermore, the expense of operating at a. high temperature is greater than in operating at a low temperature. temperature the reaction is more rapid than at a low temperature, but under some circumstances a slower reaction is desirable because the plant and eperation arefiless expensive. Thus, when the method of said atent is operated at' a temperature of 900 being substantially above the melting point of pure lithar e, 883 (3., the opera tion is very rapid. hus, lead antimony alloy containing 3.5% antimony can be reduced to an alloy containing 003% antimony in less than fifteen seconds -at a tem perature of 900 ,C. with the proper subdivision of the masses- I The object of the present invention is to produce a method of refining lead alloy,

and specifically lead antimony alloy, by the use of molten litharge at low temperatures,

and to this end the invention consists in the method hereinafter described and particularly defined in the claims.

A specific example of the invention will be described. Antimonial lead such as may be obtained as a product-of smelting scrap storage battery.pl ates, which would carry from 3% to 5% antimony, will be melted and poured into a cast iron vessel, such as with paddles secured to the walls for stirring the contents. Pulverulent litharge will be introducedinto the vessel in suitable quantity, and the .mass will litharge brought into intimate contact withthe molten lead:- On

50" mixing the litharge and lead, the litharge immediately becomesliquid and remains so during the operation of the process. The incipient accumulation of antimony by the litharge lowers its melting point sothat the reaction is carried on under molten condi- It is true that at a high Application filed January 11, 1928. Serial No. 80,671.

t ions, and the intimate admixture of the litharge and lead alloy is secured.

The reaction may be carried on in a rather deep kettle where the stirring may be done by a perforated iron or steel plunger which is raised and lowered in the kettle. Again, the stirring may be performed in such a kettle by a propeller stirrer mofiiitedon a vertical axis and supported above the kettle, having a steel ring around it so that by the rotation of the stirring propeller, the

mixture is caused by the propeller to flow downward through the ring which surrounds it and upward on the sides of the kettle, thereby securing the desired intimate mixing of the lead alloy and litharge.

The litharge employed may be pure litharge, and in such case as soon as it is mixed with the lead and its absorption of.

antimony begins, it becomes fluid, that is,

it assuiiiesa molten condition. 'But it may.

be convenient to 'use a litharge bearing a small percentage of. antimony, and to introduce it into the molten alloy in a pulverulent condition.

The amount of litharge introduced into the molten lead antimony alloy should be about three times by weight the amount of the antimony. content of the lead antimony alloy. Thus, the amount of litharge is dependent more or less upon the amount of.

antimony in the lead. There is no exact amount'of litharge required. It has been found that litharge at the end of the refining operation may contain anywhere from a comparatively small percentage of antimony, was great, up to 38% antimony, where. the amountof litharge used was less. Good working conditions would indicate the,u se

where the amount of litharge used' of such an amount of litharge as to give an antimony content afterthereaction of 23%.

The limits of temperature at which the process is worked may vary widely from a low point of approximately 600 'C., which is the melting point" of litharge carrying antimony, and a high point of approximately 883 0., which is the melting point of pure litharge. The lower temperature is a critical one, as this invention contemplates theuse of a. temperature between a lowerlimit being the melting point of antimonial litharge (approximately 600 C.) and an upper limit being the melting point of Euro litharge (approximately 883 0.). Re ning antimonial lead at temperatures below 600 C. by the use of litharge involves a process whic forms the subject matter of another application filed by the present inventor.

According to this method lead containing 3.62% antimony was reduced to a lead containing .05% antimony in fifteen minutes at a temperature of 680 C. For some uses this degree of purity is sufficient, and by reason 'of the economy of operating at a lower temperature it is to be preferred, particularly as owing to its use a smaller plant investment is required.

This process is adapted to large scale eration, and by it the greater part of tiie antimony may be removed from the lead in a short space of time. By longerworking a high degree'of" purity may be obtained. The resulting product may be subjected to a further refining process for the purpose of removing practically all of the remaining antimony content.

One of the advantages of the present process resides in the fact that the use of the'expensive magnesite lining is avoided, as the process is susceptible of being Worked in an iron pot without substantial deterioration of the latter. This contributes to the economy by whichtheprocess may be carried on.

Another advantage of the present proc ess resides in the fact that it does not reuire the use of any other substance than t e metals of the alloy to be refined and their oxides. It is a simple, uncomplicated process.

Another feature of the invention resides in the fact that no material or substance is required (nor desirable) to be introduced to lower the melting point of the litharge.

While the present invention has been described in connection with the refining of lead containing antimony, it is to be understood that it is not limited to this specific lead alloy, as it may be employed in removing other metals from lead, among which may be mentioned copper.

Having thus described the invention, what is claimed is: Y

1. The method of refining lead which consists in exposing lead alloys in molten condition to the action of litharge by causing the two materials to be exposed to each other in bodies of small dimensions and at temperatures between the melting point of litharge carrying the alloy metal and the melting point of pure litharge (approximately 883 (1).

2. The method of refining lead containing antimony which consists in subjecting the lead antimony alloy in molten condition to the action of litharge by causing the two materials to be mixed together at temperatures between the melting point of litharge carrying antimony (approximately 600 C.) and the melting point of pure 1ith.rge (approximately 883 C.).

In witness whereof I have signed my name to this specification.

PHILIP W. DAVIS. 

